Albert Einstein’s Theory of Relativity had set the speed of light as the universal speed limit of sorts, and showed that time and distance are not faithfully absolute but are affected by one’s rate of motion. A clock which is in motion always appears to run slower when compared to one at rest. This is because time is always relative to the speed at which a body is moving. This means that you could actually do a bit of time travel, but of course you need to have a really fast spaceship. Consider an astronaut traveling into space for six months at a speed that is close to speed of light, and then taking another six months to return to Earth. He would land in the future! While it would be only a year that has elapsed on the astronaut’s clock, back on Earth, tens of thousands of years would have passed, depending on how close to the speed of light the austronaught was traveling.

In a nutshell, the laws of physics allow for time travel, but the law which relates to time and space as proposed by Einstein, may have to be revised a bit by incorporating the unusual rules of quantum theory. Quantum theory illustrates the microscopic randomness which fills the universe, at the subatomic level. At these nano scales, gravity tends to go a little bit haywire, and physicists have a tough time predicting gravitational. It is theorized that space and time could eventually collapse, but the conventional notion that time will run in reverse when the universe collapses has run into somewhat of a roadblock. New researches suggest that the universe doesn’t necessarily go though a sequence of expansions and contractions and then ending up in a uniform state.

It is speculated that the universe started out in a disorderly state, then expand and finally collapse into the same very randomness that it started with. Physicists have been long puzzled about the two “arrows of time” which point in identical directions. In our everyday life, entities wear out over the course of time, for example, cups fall and shatter, but they never reassemble impulsively. In the expanding universe, the future is actually the direction of time when the directions of time of the galaxies are further part. Years ago, it was suggested that the arrows might be linked; this would mean that if the expansion of the universe is reversed, then the daily arrow would also reverse, which means broken cups would reassemble themselves, which might seem absurd to laymen, but is faintly possible in the eyes of a quantum physicist. Recently, the concept of arrow reversals has been incorporated into quantum physics. The arrow of time was associated with the so-called “collapse of the wave function”.

Some physicists have tried making this quantum description of reality and symmetry in time; they did it by coupling the original and closing states into one single mathematical equation. Of course this all sounds like science fiction, but relativists have taken the possibility of time travel very seriously, even to the point that they have proposed that there must be a law which prevents time travelers from creating paradoxes. However, nobody has the faintest idea how such a law would operate. The classic paradox is that of going back in time to alter things in such a way as to prevent one’s own birth, for instance killing one’s ancestors, or making sure that their parents never meet each other. These things simply go against common sense, argue the skeptics, so there must be a theoretical law that prevents these types of things from happening.

So what happens when Einstein’s laws are pushed to the limits? As one would expect, the possibility of time travel involves black holes. Since Einstein’s theory is a theory that deals with space and time, it shouldn’t comes as a surprise that black holes may offer a way to travel thorough time, as well as space. However, any black hole won’t do. A black hole formed out of a non-rotating lump of material would simply be devouring anything that comes near it. At its heart is a dot referred to as a singularity. This is where time and space supposedly cease to exist and matter is crushed to infinite density. In a rotating black hole things are a bit different, a singularity still forms, but it’s shaped like a ring, an ideal analogous to this would be mints which sport a hole in the middle.

At least in theory, one would be able to dive into the ring and emerge at another place at another time. In the 1980’s, Kip Thorne of CalTech and his colleagues, exasperated with trying to tackle time travel realities, set out to prove once and for all that Einstein’s equation doesn’t actually allow for time travel. They did some intense studying of the situation from a variety of perspectives; they were surprised to find that nothing in the equation actually barred time travel. They found that what would be needed is the technology to manipulate black holes. Then there are the geographically setup black hole time machines described as “wormholes”, these connect black holes at one place and time with another which is at another place and time via a “throat”.

Michio Kaku, a professor of physics in New York, has set forth an interesting depiction of a time machine. It comprises of two chambers, each with two parallel metal plates. An intense electric field created between the two pairs of plates (the intensity created would have to be larger than anything possible with today’s technology) it literally rips apart the space-time fabric, thus creating a hole in space which connects the two chambers. According to Einstein’s equation, time runs slower for a moving object. Taking advantage of this fact, one of the chambers is taken on a long, rapid journey and then brought back. Time would vary at different rates at the two ends, and anyone falling into the wormhole at one end would be instantly hurled into the past or the future. However, creating a wormhole the size of a spacecraft, and keeping it stable long enough to move one end of it into place, would require the energy equivalent of many times that which can be produced in a lifetime. Construction of wormholes would also require a rare substance known as “negative matter”, which though is not known to be totally impossible, is yet to be found to exist in a state useful for wormhole construction. Therefore it’s highly unlikely that such a device would ever be created, even with some of the most extreme technologies man can dream of, or will develop in the future.